Wrist Sniffer
Ultrasonic beacon detector
$0.99
Catch ultrasonic tracking beacons in shops, transit, and venues - the kind that pair your phone to a TV ad you just walked past. Your Watch is the mic.
Warning - the app requires paired Apple Watch to function properly.
Wrist Sniffer turns your Apple Watch into an ambient ultrasonic-beacon detector. The 17–22 kHz band is increasingly used by cross-device tracking systems - Silverpush, Lisnr, SoundPays, and similar - to pair phones to TV ads, in-store displays, kiosks, and event sound systems without your knowledge. Your wrist mic is closer to the open air than a pocketed phone, which makes the Watch a better sensor for these signals.
Open the app, tap Scan, and Wrist Sniffer listens for the distinctive spectral shape of a beacon: a narrowband tone or keyed pattern sitting well above the speech and HVAC floor, in a band human ears cannot hear. When the detector trips, the Watch taps you with a haptic and logs a spectral fingerprint to the paired iPhone for later inspection.
WHAT IT DOES
• Real-time FFT analysis of microphone input, on-device
• Three-band energy detector (5–10 kHz reference, 14–17 kHz guard, 17–22 kHz target) with configurable thresholds and hysteresis
• Haptic alerts on the Watch the moment a beacon-shaped signal is detected
• Each scan runs in an extended-runtime session so it keeps listening with the wrist down or the screen asleep, up to the watchOS session limit (roughly one hour) - useful for walking through a venue
• Spectrogram viewer and detection log on the iPhone
• JSON export of detection events for offline analysis
WHAT IT IS NOT
• Not silently background-continuous. watchOS does not allow indefinit background microphone use, and Wrist Sniffer does not try to. A scan only runs while a session you explicitly started is active, and that session ends when you stop it or when watchOS hits its time cap.
• Not a classifier of who placed the beacon. The detector flags beacon-shaped energy; distinguishing one vendor from another is an ongoing engineering effort and the detection log gives you the raw fingerprint to investigate.
PRIVACY
• Microphone input is analysed entirely on-device, on the Watch and the paired iPhone.
• No audio, no spectra, no detection events leave your devices unless you explicitly export them.
• No analytics SDKs. No third-party trackers. No accounts. No servers.
• Optional location tagging is opt-in and stored only locally.
HARDWARE
Designed for Apple Watch Series 9 and Apple Watch Ultra 2 or newer, paired with an iPhone running iOS 17 or later. Performance on older Watch hardware is limited by the microphone's high-frequency response and is not supported.
A NOTE ON LIMITS
Ultrasonic detection on a wrist microphone is a real signal-processing problem, not magic. Anti-aliasing filters, mic placement, body shadowing, and ambient noise all matter. Wrist Sniffer reports what it sees and gives you the raw spectra to second-guess it. It is a tool for the curious - a field instrument, not a guarantee.
Ratings & Reviews
- This app hasn’t received enough ratings or reviews to display an overview.
The developer, Piotr Szmielew, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Piotr Szmielew
- Size
- 2.8 MB
- Category
- Utilities
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later. - Apple Watch
Requires watchOS 10.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- Copyright
- © IT Piotr Szmielew
